The present invention relates to orientation sensing apparatus and, in particular, to apparatus for sensing the orientation of a member which is capable of several different types of movement. The invention has particular application to devices which are pivotally movable about mutually perpendicular axes, such as a gun in an arcade target shooting game which is variable in elevation and azimuth for aiming purposes.
There are several different types of target shooting games. In one type the gun fires a "projectile", such as a beam of light, which strikes the target if the gun is properly aimed. In this type of device the accuracy of the aim is directly observable, and there is no need to measure the orientation of the gun.
In another type of game which is electronically operated, the gun does not fire a "projectile". Rather, the targets are disposed at known predetermined locations, and whether a target is "hit" or not is determined by whether or not the gun is properly aimed at the target location. In order to determine this, it is necessary to sense and measure the orientation of the gun and determine whether or not the aiming direction corresponding to that orientation also corresponds to a target location.
Various types of position control mechanisms have been used in arcade games, and particularly video-type arcade games. Thus, joysticks have been utilized for controlling the movement of an object, such as a cursor on a video screen, along horizontal and vertical axes. These devices sense and record relative movement, but they cannot determine absolute position. Thus, the direction and extent of movement of the joystick or trackball device corresponds to the direction and extent of movement of a controlled object, such as a video screen cursor and, in the case of a trackball, the rate of movement of the controlled object also corresponds to the rate of movement of the trackball. But in such devices, the zero reference point is wherever the movement of the device happens to start, and there is no means for determining the position of the device with respect to a fixed or permanent reference.
There have also been provided optical systems for sensing the position of a movable object with respect to a predetermined axis, by establishing a light beam which moves with the object and sweeps an encoding grid which quantizes various positions throughout the range of movement. But such devices have not been provided for determining absolute orientation of an object which undergoes plural ranges of movement.